Douglas Krantz - Technical Writer - Describing How It Works

Can We Trip a Booster Power Supply with an SLC?

By Douglas Krantz | Life-Safety | 6 minutes of reading

Can We Trip a Booster Power Supply with an SLC?

Greetings Douglas,

Does the Fire Code allow tripping remote power supplies, such as NAC Panels, via the SLC loop on an addressable system?

Thank you, TM

This is an issue more concerned with compatibility than with the NFPA. However, to answer your question, we need some background information.


The Fire Code published by non-profit organizations like the National Fire Protection Association (NFPA) is published to show what a fire alarm system should be like when it is completed. Included with the description of the fire alarm system are some do's and don'ts about methods used to complete the system.

Mostly, though, technology is too vast and changing far too rapidly for the NFPA or any other non-profit organization to keep up with all the new ways to put a system together. Instead, the NFPA relies on the manufacturers to design a reliable fire alarm system that meets the standards shown in the NFPA.


It's not enough to just say to anyone that they should make something good, just saying that allows for conflict of interest, and fire alarm manufacturers are included in the conflict of interest. To get around the conflict of interest, the NFPA says that anything used for life safety systems has to be tested by someone else - someone that has no "skin-in-the-game", so to speak. The someone they refer to is a third party, nationally known, testing laboratory, like UL, FM, CE, ULC, etc.

With fire alarm systems, this third-party testing laboratory makes sure that the system isn't going to be a danger itself, and that the system will properly and reliably detect fires, and warn people of fire.


Nothing that the manufacturer makes can be brought to market without a stamp on it saying, in essence, "This Has Been Tested and Works Reliably". This includes the fire alarm panels, the devices that are used with the panels, and even the installation sheets that come with the panels and devices.

The installation sheets that come in the boxes with the equipment are part of the design. The wiring and even the wiring layout shown in those sheets have to be followed, or the system as it is installed is not tested and approved by the third party. In other words, even if the system works when tested on site, if these sheets are not followed the system might not be reliable in case of fire.


The word "tested" is where the word compatibility comes in. To be compatible, parts of the system, including the installation sheets, have to be tested by someone other than the manufacturer, the building owner, or even the installation company.

If the NAC panel and the fire alarm panel has been tested to be reliable when working through the SLC (Signaling Line Circuit), and the third party (like UL, ULC, CE, etc.) puts its stamp on the system (including the installation sheets) as wired, then it's compatible.


We have one other issue to deal with, and that is acceptance by the Authority Having Jurisdiction (AHJ). That becomes a very interesting issue because there are a number of AHJ's that we, as fire alarm installers, have to deal with.

According to the NFPA in their definitions, the AHJ can make a lot of decisions. In their Appendix A, the NFPA describes the AHJ as being the fire marshal, the inspectors, the insurance company representative, and in some cases, even the owner.

In the NFPA's National Fire Alarm Code Handbook, the writers and editors of the NFPA Code say that if there's a conflict between what the NFPA Code says and what an AHJ says, that we, as fire alarm installers have to install the system using the more stringent method.

Remote Tripping of NAC Power Supplies

If the manufactures of the fire panel and the NAC panel say that the NAC panel can be tripped using the SLC (Signaling Line Circuit), then it has been tested by a third party and is acceptable in the NFPA Code. If an AJH requires something more stringent (like the NAC panel can only be tripped by the main fire alarm control panel), the NFPA Code requires the more stringent installation.

Of course, the written compatibility can be shown to the AHJ, and the AHJ can have a change of mind, but in the final analysis, the AHJ makes the rules.

Douglas Krantz
Life Safety
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